Prevent a player from moving faster than usual by moving in two directions

Question

I'm messing a bit with pygame, a player can freely move around the screen with WASD and change the direction they are facing with ← and →, the problem is that they can move faster than usual if they hold two keys at once (e.g. W + D, W + A) and I was wondering what should I change to fix this.

import math
import sys

import pygame as pg


class Player:
    def __init__(self):
        self.x, self.y = 400, 300
        self.speed = 7.5
        self.rot_speed = 0.05
        self.angle = math.pi * 1.5

    def movement(self):
        cos = math.cos(self.angle)
        sin = math.sin(self.angle)
        speed_cos = self.speed * cos
        speed_sin = self.speed * sin
        dx, dy = 0, 0

        keys = pg.key.get_pressed()
        if keys[pg.K_w]:
            dx += speed_cos
            dy += speed_sin
        elif keys[pg.K_s]:
            dx -= speed_cos
            dy -= speed_sin
        if keys[pg.K_a]:
            dx += speed_sin
            dy -= speed_cos
        elif keys[pg.K_d]:
            dx -= speed_sin
            dy += speed_cos

        self.x += dx
        self.y += dy

        if keys[pg.K_LEFT]:
            self.angle -= self.rot_speed
        if keys[pg.K_RIGHT]:
            self.angle += self.rot_speed
        self.angle %= math.tau


    def draw(self):
        pg.draw.line(
            screen,
            "yellow",
            (self.x, self.y),
            (
                self.x + 100 * math.cos(self.angle),
                self.y + 100 * math.sin(self.angle),
            ),
            1,
        )
        pg.draw.circle(screen, "green", (self.x, self.y), 15)

pg.init()
screen = pg.display.set_mode((800, 600))
clock = pg.time.Clock()
player = Player()

while True:
    for event in pg.event.get():
        if event.type == pg.QUIT or (event.type == pg.KEYDOWN and event.key == pg.K_ESCAPE):
            pg.quit()
            sys.exit()

    screen.fill("black")
    player.movement()
    player.draw()
    pg.display.flip()
    clock.tick(60)

@Rabbid76 Neither of those duplicates are actually asking the same question, nor do their answers directly addresses the question here. (One of them mentions normalization, but doesn't explain why it's needed). The two question represent further problems one might encounter after solving the problem in this question, but they aren't duplicates. — MegaIng, Mar 23 '23 at 07:30
@MegaIng You are right. Anyway, I am very sure that this question is duplicated ( likely more than 100 times.) I just referred to the wrong questions. — Rabbid76, Mar 23 '23 at 09:45
@Rabbid76 https://stackoverflow.com/questions/69246646 and https://stackoverflow.com/questions/44928930 seem like good choices — MegaIng, Mar 23 '23 at 13:30
Does this answer your question? [moving diagonally makes player go faster](https://stackoverflow.com/questions/69246646/moving-diagonally-makes-player-go-faster) — MegaIng, Mar 23 '23 at 13:32

score 2 · Accepted Answer · answered Mar 22 '23 at 21:57

You need to normalize the movement vector, it will fix the problem of a player moving faster diagonaly, here is the updated code:

def movement(self):
    cos = math.cos(self.angle)
    sin = math.sin(self.angle)
    speed_cos = self.speed * cos
    speed_sin = self.speed * sin
    dx, dy = 0, 0

    keys = pg.key.get_pressed()
    if keys[pg.K_w]:
        dx += speed_cos
        dy += speed_sin
    if keys[pg.K_s]:
        dx -= speed_cos
        dy -= speed_sin
    if keys[pg.K_a]:
        dx += speed_sin
        dy -= speed_cos
    if keys[pg.K_d]:
        dx -= speed_sin
        dy += speed_cos

    magnitude = math.sqrt(dx * dx + dy * dy)
    if magnitude > 0:
        dx /= magnitude
        dy /= magnitude
        self.x += dx * self.speed
        self.y += dy * self.speed

    if keys[pg.K_LEFT]:
        self.angle -= self.rot_speed
    if keys[pg.K_RIGHT]:
        self.angle += self.rot_speed
    self.angle %= math.tau

Thanks, in case anyone else wants to use this `speed_cos` and `speed_sin` are not necessary, you can just multiply by `cos` and `tan` — qwerty_url, Mar 23 '23 at 00:51

Prevent a player from moving faster than usual by moving in two directions

1 Answers1